Linear low density polyethylene ("LLDPE") has been found useful as the film-forming component of blown stretch wrap films since it is especially strong. However, a cling additive must be blended with the LLDPE prior to film formation since LLDPE does not exhibit a high level of cling. Stretch wrap film loses peel cling when stretched. It is important that blown stretch wrap film have an adequate amount of cling when stretched to lengths of at least 200 percent elongation, for typical stretch wrapping processes.
Amorphous polyolefins having a viscosity greater than about 2,000 mPa.s at 190.degree. C. have been found to be useful as LLDPE "cast" stretch film tackifiers for providing film cling, but not useful as LLDPE "blown" stretch film tackifiers. The LLDPE film containing the amorphous polyolefins does not have adequate peel strength at 200 percent elongation.
U.S. Pat. No. 4,430,457 (Dobreski) discloses a cling additive for ethylene vinyl acetate ("EVA"), low density polyethylene ("LDPE"), or LLDPE film compositions comprising a low viscosity amorphous propylene-ethylene copolymer having about 1 to about 7 weight percent ethylene units. The particular propylene copolymer disclosed in the example in that patent is POLYPOL 19, produced and sold by Crowley Chemical Company. POLYPOL 19 copolymer has a viscosity of 50 to 120 mPa.s at 190.degree. C., a ring and ball softening point (RBSP) of 77 to 99.degree. C., and a cone penetration of 65 to 90 dmm at 21.degree. C. (needle penetration estimated by applicant to be approximately 130 to 180 dmm at 21.degree. C.) according to Crowley Chemical Company, Inc. Technical Bulletin (Jan. 10, 1994, POLYPOL 19). Dobreski discloses that blown film formed from those compositions have adequate peel cling when unstretched.